Typical vehicle exhaust systems include an exhaust pipe, a muffler, and a tail pipe. In prior systems, acoustic attenuation, or sound suppression, is substantially performed by the muffler, while the connecting pipe and the tail pipe serve primarily to transport the exhaust gas. These pipes are typically cylindrical tubes of constant cross-sectional area and may include an elbow bend or a T-shaped intersection. In some instances, the pipes themselves may add to the noise problem by creating standing waves and undesirable resonances.
Generally, a muffler's attenuating influence is related to its length and diameter; the larger a muffler is, the greater its attenuating influence. To attenuate low frequency noise, such as that produced in a truck exhaust system, a muffler must be relatively long.
Relatively long or large mufflers, however, are disadvantageous for many reasons. Long or large mufflers require a relatively large amount of steel to manufacture and therefore are relatively expensive to produce. They are relatively heavy and cumbersome and therefore relatively difficult to install and support. Perhaps most significant is that the vehicle must include a relatively large space dedicated to a relatively large muffler, thus necessitating redesign of engine placement and body design to accommodate.
One highly effective means of suppressing sound is the employment of an apparatus including a venturi contained within a housing. Such an apparatus is shown in U.S. Pat. No. 4,580,657.
It would be desirable to produce a venturi-like sound attenuating element of a reasonable size, which has relatively good sound suppression characteristics. Further, it would be desirable to create attenuating elements capable of serving as tail pipe or connecting pipe sections thus requiring less attenuating at the muffler to achieve a given attenuation which is distributed through the system as a whole.